In pressurised shaving foam dispensers of the above-mentioned type, a foamable concentrate, generally an aqueous soap solution, is contained in a dispenser equipped with a dispensing head and valve, and pressurised with a normally gaseous propellant, e.g. a low molecular weight hydrocarbon or hydrocarbon mixture or a halohydrocarbon or halohydrocarbon mixture. In the container the liquefied propellant forms an emulsion in the foamable concentrate, the emulsion being referred to as an aerosol emulsion. Upon discharge of the emulsion through the dispensing head the volatilization of the dispersed liquid droplets of propellant causes the dispensed concentrate to foam. Depending upon the precise formulation of the concentrate, the dispensed product may range from a dense creamy foam to a light lather.
For the avoidance of doubt, the term `emulsion` will be used throughout this specification and claims to refer to the whole liquid contents of the dispenser, i.e. the foamable concentrate plus liquid phase propellant, and the term `concentrate` will be used to refer to the liquid contents of the dispenser, other than the propellant, `liquid` in this context embracing solutions, emulsions and suspensions. In other words, the concentrate itself may be an emulsion or suspension and not necessarily a solution of the foam producing ingredients in a suitable liquid medium, which in the case of the present invention will be water.
Various disclosures have been made of compositions suitable for use in such dispensers, amongst which may be mentioned U.K. Pat. Specification No. 838,913 and U.S. Pat. No. 2,655,480. In accordance with the proposals of U.K. Pat. Specification No. 838,913 aqueous soap solutions are used in which the quantity of alkali metal, ammonium or alkylamine soaps, or soaps of primary or secondary alkanolamines, is kept below 4%, based on the weight of the concentrate, and in which the amount of triethanolamine soap is kept in minor proportion relative to the total soap content. In accordance with U.S. Pat. No. 2,655,480 aqueous soap solutions are also used, the actual concentration varying with the particular soap used. Thus, when triethanolamine stearate is used the concentration may be from 2-30% by weight of the solution and when potassium stearate is used the recommended amount is from 5 to 20%. A generally recommended range for all soaps is 5 to 18%.
Yet other aqueous soap solutions are disclosed in U.S. Pat. No. 2,908,650, these being aqueous solutions of alkali metal soaps and soaps of nitrogen bases in specified proportions.
In such prior compositions a variety of additives have been proposed or used to modify or control the properties of the foam or emulsion. For example, U.S. Pat. No. 2,655,480 discloses that water-soluble non-ionic or anionic wetting agents may be added in amounts up to 5 or 6%, based on the weight of the concentrate, to facilitate rinsing of the lather from the face and avoiding oily deposits on the skin. Particular anionic and non-ionic wetting agents mentioned are sodium lauryl sulphate, sodium dodecyl benzene sulphonate, and watersoluble polyoxyethylene ethers of alkyl-substituted phenols. In addition, glycerine may also be added to stabilize the lather. U.K. Pat. Specification No. 838,913 discloses the addition of small amounts (1-3%) of water-soluble emulsifiers, e.g. fatty acid esters of polyhydricpolyoxyethylenated alcohols and fatty acid alkanolamides. U.K. Pat. No. 838,913 also discloses the addition of water-insoluble fatty acids, fatty alcohols and their ethylene oxide derivatives, to give the lather a creamy character and effect a slight fatting of the skin. In addition, U.K. Pat. No. 838,913 further teaches the addition of relatively high amounts (up to 15%) of water-insoluble free fatty acid to effect stabilization of the lather.
Reference may also be made to the studies reported in J.Soc. Cosmetic Chemists, 17, (1966), pages 801-830 on the effects of the addition of long chain fatty alcohols to aqueous aerosol emulsions based on anionic surfactants, in particular, on certain triethanolamine soaps and on sodium lauryl sulphate. In general, the addition of long chain alcohols to these emulsions showed an increase in viscosity and emulsion stability, judged on the time required for phase separation after hand shaking. Increases were also noted in foam stability and foam stiffness.
Although soap-based aerosol shaving foams have attained a certain degree of popularity, the formulations currently used have certain disadvantages, the foremost of which is the tendency, when used, to form a scum either in the form of hardwater deposits, particularly, of course, when used in hard water areas, or in the form of free fatty acid. This scum, in turn, forms unsightly deposits around the wash basin and, more particularly, on the razor and because of the difficulty of removing these deposits, which are often not removed by simple rinsing, the razor rapidly becomes encrusted.
Soapless aerosol foams based on synthetic surfactants and containing a synthetic surfactant in combination with a long chain fatty acid or alcohol have been described. For example, in Soap and Chemical Specialities, July 1967, pages 70-78 and 162, continued in Soap and Chemical Specialities, Aug. 1967, pages 70-74, 104 and 106, and in J.Soc. Cosmetic Chemists 20, (August 1969) 577-593, Sanders describes a series of studies on aerosol emulsion systems based on certain polyoxyethylene fatty ethers in combination with certain long chain fatty acids and alcohols. Again, increases in emulsion viscosity and stability and increases in foam stability and stiffness were noted. Whilst, since such systems are soap free, the problem of hard water scum does not arise, it has been found that such systems have a particular disadvantage in that they lack storage stability, particularly at moderately elevated temperatures, e.g. 30.degree.-40.degree.C, which in practice may well occur when the products are stored or placed on display, for example, in a shop window exposed to bright sunlight or are used in a hot climate. Under these conditions, compositions containing a synthetic surfactant solution and a long chain fatty alcohol or acid, as described in these articles, undergo an irreversible phase separation, that is to say they cannot be redispersed merely by hand shaking by the user, with the result that the emulsion no longer foams, or foams inadequately upon discharge from the container. Such products therefore lack the necessary shelf-life. In addition, separated solid phase material may block the valve and discharge apertures and thus further contribute to the malfunction of the container.
Other aerosol emulsions based on synthetic surfactants that have been tested suffer from other defects such as emulsion instability, noisy discharge from the container, inadequate foam formation and foam stability.